The figure above depicts the original study design with the revisions indicated by the red "Xs." The revised study involves a randomized, controlled clinical trial, test-retest design, with a six week follow up using one study arm (TBC Eligible for stabilization (STB) exercises) and 3 treatment protocols [STB, Movement System Impairment (MSI) Classification Specific, Strengthening/Conditioning (STC)]. The PI and recruitment coordinator will be blinded to treatment group assignment. Measures of pain (verbal Numeric Pain Rating Scale), functional ability (Oswestry Disability Scale), and health status (SF-36) at 6 weeks post-treatment will be the primary outcome measures in comparing the effects of the two 'patient-matched'treatments (TBC-eligible assigned to STB;TBC-eligible assigned to MSI classification-specific exercises) to the non-specific exercise protocol (TBC-eligible receiving STC). Measures related to neuromuscular control (force and real-time ultrasound imaging variables) will be characterized during automatic postural responses to support surface translations and during a voluntary task (the abdominal drawing maneuver). These measures will be assessed before and after treatment in patients in order to characterize any underlying neuromuscular impairments prior to treatment and to quantify any changes immediately post-treatment at 6 weeks. 3 Low back pain (LBP) is a musculoskeletal condition that affects up to 80% of all people at some point in their lifetime, with an annual incidence in the U.S. population of 15-45% 6. As many as 85% of people who suffer from LBP experience recurring symptoms 6, a propensity for chronic pain that likely reflects ineffective treatment. No clear evidence supports any one treatment for LBP, perhaps because past studies examined heterogeneous groups of subjects with LBP. Thus, it is essential that we classify homogeneous subgroups of people with LBP based on relevant measures of impairment 9,14,82. Accurate schemas of LBP classification could allow clinicians to match patients to the most appropriate treatment, potentially resulting in superior and more efficient treatment outcomes at a reduced cost. The proposed studies focus on 2 schemas to classify LBP: 1) the Treatment-Based Classification (TBC) system, from which clinical prediction rules about who is most likely to benefit from spinal stabilization exercises have been developed, and 2) the Movement System Impairment-Based Classification (MSI) which includes 5 subgroups of LBP named for specific direction(s) of movements and alignments associated with the person's LBP. The primary purpose of this proposal is to conduct a prospective, randomized, controlled Phase II clinical trial in order to examine whether treatment matched to the patient's specific signs and symptoms per the TBC and MSI systems is more effective than a non-specific strengthening/conditioning (STC) exercise protocol for improving short-term (6 weeks) outcomes (neuromuscular impairments, pain, function, and health status) in people with chronic LBP. Subjects who are TBC-eligible for stabilization exercises will be randomly assigned to 1 of 3 exercise protocols for a 6-week period: 1) stabilization - a protocol focused on improving the motor control of trunk muscles to stabilize the spine;2) MSI-based - a classification-specific treatment focused on education and instruction for modifying movement strategies during functional activities, and on exercises specific to the classification category;or 3) a non-specific STC exercise protocol. Laboratory measures (real-time ultrasound imaging and forces) during standardized tasks will quantify neuromuscular impairments associated with LBP and clinical questionnaires will quantify changes in pain, function, and health status pre- and post-treatment. This series of experiments will, for the first time, compare two classification systems used in LBP treatment and determine if they are superior to STC exercises. 4